Most metallic and many plastic surfaces of useful articles are painted to prevent weathering and corrosion and for decorative reasons. One common way to paint a large object, e.g. an automobile or automobile part, is by using a housing or booth in which the paint is sprayed on the object. The object then usually remains in the booth while the paint is cured by heating or other means. Such paint spray booths are commonly prefabricated building structures having a ceiling, floor and walls that define an interior space large enough to hold the object to be painted, with sufficient room on all sides for workmen to effectively operate paint spray and other equipment. These booths provide advantages such as reducing particulates, confining paint overspray and evaporated solvents and reducing drying times.
One common type of paint spray booth is the downdraft and semi-vertical spray booth that uses a housing positioned over an open floor grate or an exhaust outlet near the bottom of the walls. Air from the ceiling and any entrained paint overspray and solvents are drawn downward over the vehicle during spraying and drying and are then exhausted through the floor grate or exhaust opening. One example of such a spray booth is described in U.S. Pat. No. 6,533,654, incorporated herein by reference. Curing of the paint applied to the object is usually accomplished by using heaters to increase the temperature within the booth. The paint curing time in conventional paint spray booths may take about one hour.
Materials that are cured (hardened) by exposure to light have recently shown promise in a variety of industries because such materials have very short cure times without the application of heat, and have several advantages in speed and ease of use. Some of the general benefits of light-cured materials include rapid curing times (in some cases almost instantaneous, allowing for immediate further processing), on demand curing (requiring only exposure to UV light), no solvents (100% solids—no environmental pollution due to solvent evaporation), no heat (low thermal stressing of substrate materials), single component systems (ready-to-use with no mixing, no waste, no cleaning of mixing containers, no problems with pot life or mixed materials, no dangerous isocyanate catalysts), and more efficient use of raw materials and energy. Examples of light-cured materials include structural adhesives for bonding glass, ceramics, ferrites, plastics and metals; UV hot melt pressure sensitive adhesives; UV glob tops, chip coats and conformal coatings; UV potting compounds and encapsulants; UV paints, inks and coatings; and UV hardening polyester resin/glass fiber composite materials.
The use of light-cured materials can be found in an extremely wide variety of industries such as, for example, the electronics, printing, furniture, floor covering, medical device, dental, packaging, marine and paper industries. The use of light-cured paints and coatings in the automotive refinish and repair markets has grown considerably in recent years, but to date has typically been limited to primer applications. However, it is likely that light-cured products will be expanded to possibly include basecoats, topcoats, fillers and glazes, adhesives and sealers.
Light-cured materials contain chemicals known as photo initiators that comprise certain reactive groups, e.g. acrylate or methacrylate groups, which are sensitive to UV radiation. When photo initiators are illuminated with intense UV light, they initiate a polymerization reaction that hardens the material. If a light-cured material is used as a paint or other coating to cover an object, the hardened material provides a protective finished surface, or one that is ready for sanding and application of other coats in a short period of time, e.g. in about 2-5 minutes.
Curing of light-cured materials currently requires the use of a UV lamp. These UV lamps typically use a relatively small high-intensity discharge (HID) quartz bulb that is filled with mercury and traces of other elements. A high voltage applied to electrodes in the lamp creates an arc that heats the gaseous atoms to the point at which they emit UV light, visible light and infrared light. Full intensity is usually reached within about 2-5 minutes. The bulb is positioned inside a reflector that collects and focuses the light toward the lamp opening, which is typically designed to filter out more-harmful UV-B and UV-C radiation and allow only UV-A radiation to be emitted by the lamp.
UV-curing lamps have certain disadvantages. In addition to being relatively expensive, the HID bulbs slowly decrease in light output over time (thereby causing progressively longer cure times) and should be replaced after about 500 hours of use. It is recommended to turn off the bulb immediately after each use to maximize bulb life, minimize stray UV radiation, heat buildup in the workplace, and make the lamp easier to handle and move. UV-curing lamps are intended to be used only in a restricted area, accessed only by qualified professional operators, due to the dangers of being exposed to the emitted UV radiation and the generation of ozone by the lamp. In addition, UV lamps generally only have a very limited exposure area or footprint. Currently the coverage area of UV-curing lamps may be limited to an area of about 6 square feet, which results in frequent repositioning of the lamp. Although this disadvantage may be limited somewhat by mounting the lamp on a computer guided robot which automatically repositions the lamp to a different exposure area, this solution is very expensive.